Compressive Graft Fit Promotes Tendon-to-Bone Integration After Anterior Cruciate Ligament Reconstruction

Background: Tendon graft integration with adjacent bone in the tunnels after anterior cruciate ligament reconstruction (ACLR) is critical to reach presurgical functional levels and achieve long-term surgical success. Unfortunately, tunnel integration does not always occur, resulting in complications attributed to cyst formation and tunnel widening, necessitating revision surgery. Previous studies have indicated that mechanical factors, including fit of the graft in the tunnel, can influence healing, but the extent to which graft fit facilitates tendon-to-bone integration is unclear. Purpose/Hypothesis: The purpose of this study was to investigate the effect of graft fit in the tunnel on zonal tendon-to-bone integration in a murine ACLR model. It was hypothesized that a tight-fitting graft would promote integration and reduce cyst formation. Study Design: Controlled laboratory study. Methods: ACLR surgery was performed in a compressive-fit group of mice using 27G needles (0.413-mm outer diameter) and 1 mm–diameter tendon autografts. The fit of the graft in the tunnels was modified to a loose fit in additional groups by either increasing the size of the tunnel (25G needle, 0.515-mm outer diameter) or decreasing the size of the graft (0.5 mm). The initial fit of the graft in the tunnel was assessed during surgery using a dynamometer. The extent of tunnel integration via mineralized fibrocartilage formation and cyst formation was measured at 28 days after surgery using multiplexed mineralized cryohistology. Results: As expected, the compressive-fit group resulted in a higher friction force required to pull the graft through the tunnel during surgery, and tunnels drilled with a 25G needle were wider than 27G tunnels at 28 days after surgery. The compressive fit in the tunnels improved tunnel integration, as assessed by mineralized fibrocartilage formation normalized to tunnel dimensions. Conversely, loose-fit tunnels resulted in higher overall cyst formation when normalized to tunnel dimensions. In particular, wider tunnels correlated with higher cyst formation. Conclusion: Tendon-to-bone integration was improved by creating a compressive fit of the soft tissue tendon graft in the tunnel while minimizing cyst formation as compared with loose-fit grafts. Therefore, the fit of the graft in the bone tunnel is an important consideration for enhancing zonal tendon-to-bone integration. Clinical Relevance: This study demonstrates that a compressive fit of a soft tissue tendon graft to the bone tunnel during ACLR resulted in improved zonal tendon-to-bone integration, providing evidence that sizing grafts toward a compressive fit could improve clinical outcomes.